CN104755703A - Unducted thrust producing system - Google Patents

Abstract

An unducted thrust producing system has a rotating element with an axis of rotation and a stationary element. The rotating element includes a plurality of blades each having a blade root proximal to the axis, a blade tip remote from the axis, and a blade span measured between the blade root and the blade tip. The rotating element has a load distribution such that at any location between the blade root and 30% span the value of [Delta]RCu in the air stream is greater than or equal to 60% of the peak [Delta]RCu in the air stream.

Description

Unducted Thrust Generation System

Cross References to Related Applications

This application is related to PCT/US13/XXXXX, filed October 23, 2013, attorney docket No. 264549-2, entitled "Unducted Thrust Generation System Architecture," and attorney Docket No. 265517-2, PCT/US13/XXXXX entitled "Vane Assemblies for Propulsion Systems."

Background technique

The technology described in this specification relates to an unducted thrust generating system, in particular for spanwise aerodynamic load distribution of rotating elements mated with stationary elements. This technique is particularly beneficial when applied to "open rotor" gas turbine engines.

Gas turbine engines utilizing an open rotor design architecture are known. Turbofan engines operate on the principle that a central gas turbine core drives a bypass fan positioned at a radial position between the engine's nacelle and the engine core. Open rotor engines, on the other hand, operate on the principle that the bypass fan is positioned outside the engine nacelle. This allows the use of large fan blades that can act on larger air volumes than turbofan engines, and thus improves propulsion efficiency compared to conventional engine designs.

Optimum performance has been found in the case of an open rotor design with the fan provided by two counter-rotating rotor assemblies each carrying an array of airfoil blades positioned outside the nacelle. As used in this specification, "reverse relationship" means that the blades of the first and second rotor assemblies are arranged to rotate in counter-rotation with respect to each other. Typically, the blades of the first and second rotor assemblies are arranged to rotate in opposite directions about a common axis and are axially spaced apart along that axis. For example, respective blades of a first rotor assembly and a second rotor assembly may be coaxially mounted and spaced apart, the blades of the first rotor assembly configured to rotate clockwise about an axis and the blades of the second rotor assembly configured to rotate about the axis Rotate counterclockwise (or vice versa). In appearance, the fan blades of an open rotor engine resemble the propeller blades of a conventional turboprop engine.

The use of counter-rotating rotor assemblies creates technical difficulties in transferring power from the power turbine to drive the airfoil blades of the respective two rotor assemblies in opposite directions.

It would be desirable to provide an open rotor propulsion system that utilizes a single rotating propeller assembly similar to conventional bypass fans, which reduces design complexity and yields equivalent or Better propulsion efficiency levels than that.

Contents of the invention

An unducted thrust generating system has a rotating element with an axis of rotation and a stationary element. The rotating element includes a plurality of blades each having a blade root located near the axis, a blade tip remote from the axis, and a blade span measured between the blade root and the blade tip . The rotating element has a load distribution such that the value of ΔRCu in the airflow is greater than or equal to 60% of the peak ΔRCu in the airflow at any location between the blade root and 30% span.

Description of drawings

The accompanying drawings, which are incorporated in and constitute a part of this patent specification, illustrate one or more embodiments and together with the description explain these embodiments. In the attached picture:

Figure 1 shows a cross-sectional front view of an exemplary unducted thrust generating system;

2 is an illustration of an alternate embodiment of an exemplary airfoil assembly for an unducted thrust generating system;

Figure 3 depicts a vector diagram showing Cu passing through two rows for two exemplary embodiments;

4 graphically depicts the aerodynamic rotor load distribution for two exemplary embodiments of an unducted thrust generating system compared to a conventional configuration;

FIG. 5 graphically depicts exit swirl velocity and axial velocity for two exemplary embodiments of an unducted thrust generating system as compared to two conventional configurations;

Figure 6 graphically depicts how various parameters such as camber and stagger angle are defined relative to a blade or airfoil;

FIG. 7 graphically depicts representative parameters associated with an exemplary embodiment of an airfoil blade as compared to a conventional airfoil blade;

FIG. 8 is a front view of an exemplary airfoil blade for an unducted thrust generating system, with section line positions 1 through 11 identified; and

9 to 19 are cross-sectional views of the example airfoil blade of FIG. 8 at section line positions 1 to 11 compared to a similar section through the previously referenced conventional airfoil blade.

detailed description

In all of the following views, like reference numerals are used to refer to like elements throughout the various embodiments depicted in the figures.

FIG. 1 shows a cross-sectional elevation view of an exemplary unducted thrust generating system 10 . As can be seen from FIG. 1 , the unducted thrust generating system 10 is in the form of an open rotor propulsion system and has a rotating element 20 depicted as a propeller assembly comprising The central longitudinal axis 11 of the array of blades 21 . In the exemplary embodiment, unducted thrust generating system 10 also includes a non-rotating stationary element 30 comprising an array of fins 31 also disposed about central axis 11 . These fins may be arranged such that they are not all spaced an equal distance from the propeller, and may alternatively comprise an annular shroud or duct (duct) 100 away from the axis 11 (as shown in FIG. 2 ) or may It is unshielded. These fins are mountable to a fixed frame and do not rotate relative to the central axis 11 . For illustrative purposes, FIG. 1 also depicts a forward direction indicated by arrow F. As shown in FIG.

As shown in FIG. 1 , the exemplary unducted thrust generating system 10 also includes a drive mechanism 40 that provides torque and power to the rotating element 20 through a transmission 50 . In various embodiments, the drive mechanism 40 may be a gas turbine engine, an electric motor, an internal combustion engine, or any other suitable source of torque and power, and may be positioned adjacent to the rotating element 20 or may utilize a suitably configured transmission 50 remote location. Transmission 50 transmits power and torque from drive mechanism 40 to rotating element 20 and may include one or more shafts, gearboxes, or other mechanical or fluid drive systems.

The airfoil blades 21 of the rotating element 20 are sized, shaped, and configured so that when the rotating element 20 rotates about the longitudinal axis 11 in a given direction, by causing a working fluid such as air to flow along Move in direction Z to generate thrust. In this way, the vanes 21 cause the fluid to swirl to a certain extent as it travels in the direction Z. The fins 31 of the stationary element are sized, shaped, and configured to reduce the swirl magnitude of the fluid so as to increase the kinetic energy to generate thrust to provide a given shaft power input to the rotating element. For blades and airfoils, the span is defined as the distance between the root and the tip. Wing 31 may have a shorter span than blade 21, as shown in FIG. 1, for example, 50% of the span of blade 21, or may have a longer span than blade 21 or the same wingspan as blade 21 as required. exhibition. The airfoil 31 may be attached to the aircraft structure associated with the propulsion system, as shown in FIG. 1 , or to another aircraft structure such as a wing, pylon, or fuselage. The vanes 31 of the stationary element may be less, greater or equal in number than the blades 21 of the rotating element, and are generally greater than two or greater than four in number.

The vanes 31 of the stationary element 30 may be positioned aerodynamically upstream of the blades 21 so as to act as counter-vortex vanes, ie to generate a tangential velocity opposite to the direction of rotation of the rotating element 20 . Alternatively, and as shown in FIG. 1 , the vanes 31 may be aerodynamically positioned downstream of the blades 21 so as to act as swirl-removing vanes, i.e., causing a change in tangential velocity which is related to that of the rotating element 20. The change of the tangential velocity is opposite. Any vortex remaining in the air flow downstream of the propulsion system 10 is equivalent to a loss of thrust to generate kinetic energy.

It may be desirable that either or both of the plurality of sets of blades 21 and airfoils 31 incorporate a pitch variable mechanism such that the blades and airfoils may rotate relative to the pitch axis of rotation, either individually or together. Such pitch variation may be used to vary thrust and/or vortex effect in a variety of operating conditions, including providing reverse thrust characteristics that may be useful in certain operating conditions, such as when an aircraft is landing.

Figure 3 plots the variation of Cu across rotating and stationary elements, where Cu is the circumferential mean tangential velocity. The vector diagram is shown in a coordinate system in which the axial direction is in the downward direction and the tangential direction is left to right. Multiplying Cu by the airflow radius R yields the characteristic RCu. A blade or airfoil loaded at a given radius R is now defined as the change in RCu across the row of blades (at a constant radius or along the flow duct), hereafter referred to as ΔRCu and is the fundamental specific torque of said row of blades measure. It is desirable that the ΔRCu for the rotating element should be in the direction of rotation throughout the span.

FIG. 4 is a graph of aerodynamic load distribution versus wingspan for rotating elements 20 of an exemplary unducted thrust generating system 10 . Figure 4 shows three curves. The curve with diamonds is the load distribution for a conventional propeller assembly optimized for minimal wasted/unused kinetic energy for a single rotary propeller without a swirl removal system. The curves with squares and the curves with triangles are the load distributions for the exemplary embodiment of the unducted thrust generating system 10 described in this specification. As shown in Figure 4, the two curves for the exemplary embodiment have a more uniform ΔRCu over the span, especially in the region between the blade root and mid-span. In fact, the value of ΔRCu at the position of 30% of the span is greater than or equal to 60% of the maximum value of ΔRCu, preferably greater than or equal to 70% of the maximum value of ΔRCu, and more preferably greater than or equal to the maximum value of ΔRCu 80% of. [Delta]RCu is measured in a conventional manner across the rotating element (row of propeller blades). The blades 21 are sized, shaped, and configured to transfer this load distribution using techniques known to those skilled in the art.

The exemplary embodiments described in this specification depict specific distributions of ΔRCu across blades of rotating elements or propeller assemblies including stationary elements including removing or upstream counter-swirl vanes. During the design process, the ΔRCu will be used with the aircraft flight speed, the rotational speed of the rotor, and the total thrust required from the assembly to define the vector diagram of the air.

Figure 5 depicts the swirl, Cu, and axial velocity Vz at the outlet of an unducted thrust generating system. Figure 5 shows four curves. The curves with diamonds and the curves marked with an "x" are for two conventional configurations, a rotor only and a conventional rotor with swirl removal vanes, respectively. Curves with squares and curves with triangles are used for the two exemplary embodiments described in this specification. These embodiments have less exit swirl and more uniform axial velocity than conventional configurations, indicating less wasted kinetic energy in the exit flow and more energy converted to useful thrust.

Figure 6 graphically depicts how various parameters such as camber and stagger angle are defined relative to the blade or airfoil. The airfoil centerline is described as the line that bisects the thickness of the airfoil (or is equidistant from the suction and pressure surfaces) at all locations. The centerline runs through the airfoil at the leading and trailing edges. The camber of an airfoil is defined as the change in angle between a tangent to the airfoil centerline at the leading edge and a tangent to the airfoil centerline at the trailing edge. The stagger angle is defined as the angle formed by the chord line and the centerline axis. Reference line 44 is parallel to axis 11 and reference line 55 is orthogonal to reference line 44 .

In addition to the benefit of noise reduction, the duct 100 shown in FIG. 2 provides the vibrational response and structural integrity benefits of the fixed fins 31 by coupling the fixed fins 31 into an assembly that forms an annular ring or a or a plurality of circumferential segments, ie segments forming parts of an annular ring joining together two or more fins 31 such as pairs forming a doublet. The duct 100 allows the pitch of the airfoil to be varied as desired.

A considerable portion, perhaps even a major portion, of the noise produced by the disclosed fan principle is related to the turbulence and wake generated by the upstream blade-row and its acceleration and impact on the downstream blade-row surface ( wake) are associated with interactions between them. By introducing a partial duct acting as a shroud on the fixed fin, noise generated at the fin surface can be screened out to effectively create a shadow zone in the far field, reducing overall annoyance. When the duct is extended in axial length, the efficiency of acoustic radiation through the duct is further affected by the phenomenon of acoustic cut-off, which, as for conventional aircraft engines, can be used to confine the acoustic radiation into the far field. Furthermore, the introduction of shrouds allows for the opportunity to incorporate acoustic treatment, as is currently done for conventional aircraft engines, to attenuate sound as it reflects or otherwise interacts with liners. By introducing acoustically treated surfaces on the inside of the shroud and on the hub surface upstream and downstream of the fixed fins, multiple reflections of sound waves emanating from the fixed fins are substantially attenuated.

After the design process, the blade geometry will be defined, which forms the expected vector diagram as shown in FIG. 3 . Although the fundamental desired characteristic is the torque distribution, this will result in a blade geometry designed to obtain the desired torque distribution. A view of the changes in geometry required to produce the desired torque characteristics when compared to the current optimum conditions for a single rotary propeller without swirl removing vanes is shown in FIG. 7 . It can be seen that this results in a change in the blade camber in the inner portion of the blade, i.e. from about 0% span to about 50% span, and it is expected that the properties of the exemplary embodiments can also be Loosely defined by the camber distribution. At least one of the following conditions is met: the blade camber at 30% span is at least 90% of the maximum camber level between 50% and 100% span; and the 0% span camber is between 50% and 100% At least 110% of the maximum camber between spans.

FIG. 8 is a front view of an exemplary airfoil blade 21 , such as that depicted in FIG. 1 for use with an unducted thrust generating system as described in this specification, section line Positions 1 to 11 are determined such that section 1 is the blade tip and section 11 is the blade root. Blade span is measured between root and tip. FIGS. 9 to 19 successively show the airfoil blade section at section line positions 1 to 11 for the exemplary airfoil blade 21 and a similar section through the previously referenced conventional airfoil blade. As shown in this series of views, the two airfoil blades have sections that are increasingly different in size, shape, and orientation in the direction from section 1 to section 11 , ie, from tip to root. In other words, the area of greatest difference between the exemplary airfoil blade and a conventional airfoil blade is near the hub, consistent with the greatest difference in load distribution.

It is contemplated to utilize the techniques described in this specification in combination with the techniques described in commonly assigned co-pending applications [] and [].

In addition to configurations suitable for use with conventional aircraft platforms intended for horizontal flight, the techniques described in this specification may also be used in helicopter and tilt rotor applications and other lift and hover devices.

Other possible configurations include those designed to extract energy from airflow and generate useful torque, such as windmills that use the torque generated by extracting energy from air moving past their location to drive a generator and generate electricity. Such configurations may include upstream reverse swirl vanes.

The techniques described in this specification are particularly beneficial for aircraft cruising with shaft power above 20 SHP/ ^ft2 (shaft horse power per square foot) per unit of annular area, where vortex losses become Obvious. Loads of 20 SHP/ ^ft2 or more allow the aircraft to cruise at Mach numbers above Mach 0.6 without requiring excessive propeller area to limit vortex losses. One of the main benefits of this invention is its ability to achieve high shaft power per unit of annular area without significant vortex loss penalties, and this opens up the possibility of cruising at or above Mach 0.8 possibility.

Exemplary embodiments disclose a propeller assembly for a propulsion system. The propeller assembly includes a plurality of propeller blades, each of the plurality of propeller blades has a blade root located near the axis of rotation, a blade tip distal from the axis, and a blade tip measured between the blade root and the blade tip span. The propeller assembly has a load distribution such that the value of ΔRCu at any location between the blade root and 30% span is greater than or equal to 60% of the peak ΔRCu, preferably the value of ΔRCu at 30% span Greater than or equal to 70% of peak ΔRCu.

The foregoing description of embodiments of the present invention has been provided for purposes of illustration only, and is not intended to limit the scope of the invention as defined in the appended claims.

This application is related to PCT/US13/XXXXX, filed October 23, 2013, attorney docket No. 264549-2, entitled "Unducted Thrust Generation System Architecture," and attorney Docket No. 265517-2, PCT/US13/XXXXX entitled "Airfoil Assemblies for Propulsion Systems," the entire contents of both documents are hereby incorporated by reference into this specification.

Claims (33)

1. An unducted thrust generating system comprising a rotating element having an axis of rotation and a stationary element, the rotating element having a plurality of blades, each of the plurality of blades having a the blade root near the axis, the blade tip away from the axis, and the blade span measured between the blade root and the blade tip, wherein the rotating element has a load distribution such that Anywhere between the root and 30% span, the value of ΔRCu in the airflow is greater than or equal to 60% of the peak ΔRCu in the airflow. 2. An unducted thrust generating system comprising a rotating element having an axis of rotation and a stationary element, the rotating element having a plurality of blades, each of the plurality of blades having a the blade root near the axis, the blade tip away from the axis, and the blade span measured between the blade root and the blade tip, wherein the rotating element has a load distribution such that Anywhere between the root and 30% span, the value of ΔRCu in the airflow is greater than or equal to 70% of the peak ΔRCu in the airflow. 3. An unducted thrust generating system comprising a rotating element having an axis of rotation and a stationary element, the rotating element having a plurality of blades, each of the plurality of blades having a the blade root near the axis, the blade tip away from the axis, and the blade span measured between the blade root and the blade tip, wherein the rotating element has a load distribution such that Anywhere between the root and 30% span, the value of ΔRCu in the airflow is greater than or equal to 80% of the peak ΔRCu in the airflow. 4. A thrust generating system according to any one of claims 1 to 3, wherein the unducted thrust generating system is a thruster system. 5. The thrust generating system according to any one of claims 1 to 3, wherein the unducted thrust generating system is an open rotor system. 6. The thrust generating system according to any one of claims 1 to 3, wherein said fixed element has a plurality of fins, each of said plurality of fins has a The airfoil root near the airfoil, the airfoil tip away from the axis, and the airfoil span measured between the airfoil root and the airfoil tip, the airfoil is configured such that the tangential velocity of the air A change occurs which is opposite to the change in the tangential velocity of the air caused by the rotating element. 7. The thrust generating system of claim 6, wherein the vane is positioned upstream of the rotating element. 8. The thrust generating system of claim 6, wherein the vane is positioned downstream of the rotating element. 9. The thrust generating system of claim 6 wherein said airfoils are variable in pitch. 10. The thrust generating system of claim 6, wherein at least one of said airfoils includes a shroud remote from said axis. 11. The thrust generating system of claim 6, wherein Cu in the air stream at the rear of the system is in contrast to that of the rotating element over a majority of the span of the airfoil. ΔCu is relatively low in comparison. 12. The thrust generating system of claim 6, wherein at least one of the airfoils is attached to an aircraft structure. 13. The thrust generating system of claim 6, wherein the fixed element comprises more than two fins. 14. The thrust generating system of claim 13, wherein the fixed element comprises more than four fins. 15. The thrust generating system according to any one of claims 1 to 3, wherein the unducted thrust generating system is a tilted rotor system. 16. The thrust generating system according to any one of claims 1 to 3, wherein the unducted thrust generating system is a helicopter hoisting system. 17. A thrust generating system according to any one of claims 1 to 3, wherein the rotating element is driven via a torque generating device. 18. The thrust generating system of claim 17, wherein said torque generating device is selected from the group consisting of electric motors, gas turbines, gear drive systems, hydraulic motors, and combinations thereof. 19. The thrust generating system of any one of claims 1 to 3, wherein the rotating element has a shaft power per unit annular area of greater than about 20 SHP/ ^ft2 in cruise operating conditions. 20. The thrust generating system according to any one of claims 1 to 3, wherein the blades are variable in pitch. 21. An unducted thrust generating system comprising a rotating element having an axis of rotation and a stationary element, the rotating element having a plurality of blades, each of the plurality of blades having a a blade root near said axis, a blade tip away from said axis, and a blade span measured between said blade root and said blade tip, wherein said blade has characteristics selected from the group consisting of Said set includes: the blade camber at 30% span is at least 90% of the maximum blade camber between 50% span and 100% span, said blade camber at 0% span is between 50% span and 100% At least 110% of said maximum blade camber between % span, and combinations thereof. 22. The thrust generating system of claim 21 , wherein said stationary element has a plurality of fins, each of said plurality of fins having a fin root located near said axis, away from the airfoil tip of the axis, and the airfoil span measured between the airfoil root and the airfoil tip, the airfoil is configured such that the tangential velocity of the air varies with The change in the tangential velocity of the air caused by the rotating elements is opposite. 23. The thrust generating system of claim 22, wherein the airfoil is positioned upstream of the rotating element. 24. The thrust generating system of claim 22, wherein the airfoil is positioned downstream of the rotating element. 25. The thrust generating system of claim 22, wherein at least one of the airfoils includes a shroud remote from the axis. 26. The thrust generating system of claim 22, wherein Cu in the air stream at the rear of the system is in contrast to that of the rotating element over a majority of the span of the airfoil. ΔCu is relatively low in comparison. 27. The thrust generating system of claim 21 wherein said unducted thrust generating system is a thruster system. 28. The thrust generating system of claim 21 wherein said unducted thrust generating system is an open rotor system. 29. An unducted torque-generative system for extracting energy from a flow of air, the torque-generative system comprising a rotating element having an axis of rotation and a stationary element, the rotating element having a plurality of blades, the plurality of Each of the blades has a blade root located near the axis, a blade tip remote from the axis, and a blade span measured between the blade root and the blade tip, wherein the rotating element Having a load distribution such that at any location between the blade root and 30% span the value of ΔRCu in the airflow is greater than or equal to 60% of the peak ΔRCu in the airflow. 30. The torque-generative system of claim 29, wherein the torque-generative system is a wind turbine. 31. The torque generating system of claim 29, wherein said stationary member has a plurality of fins, each of said plurality of fins having a fin root located near said axis, away from the airfoil tip of the axis, and the airfoil span measured between the airfoil root and the airfoil tip, the airfoil is configured such that the tangential velocity of the air varies with The change in the tangential velocity of the air caused by the rotating elements is opposite. 32. The torque generating system of claim 31 wherein said vane is positioned upstream of said rotating element. 33. The torque generating system of claim 31 wherein said vane is positioned downstream of said rotating element.